The present invention relates, in general, to a device for calibrating a magnetic resonance imaging system and, in particular, to a multislice phantom for determining slice thickness, slice location and contiguity between slices.
Most prior art imaging systems involve the use of radiation in the form of X-rays and the like. There are many methods for evaluating the performance of an imaging system with respect to a number of parameters such as uniformity, linearity, spatial resolution, count efficiency and image distortion. A device known as a phantom is commonly utilized as a calibration device.
U.S. Pat. No. 4,280,047 discloses one form of phantom comprising a rectangular sealed container filled with a liquid to simulate clinical scattering. The container surrounds five interior steps extending across its width in a linear depth progression. Identical groupings of lead disks are placed on each step and each group includes several subgroups of disks arranged across the step in a linear progression of width sizes and spacings. The disks absorb radiation from a known source to a predetermined degree such that a reading from the system can be compared with a standard reading that should be obtained with the phantom.
Another form of absorption resolution testing device is shown in U.S. Pat. No. 4,323,782. This device includes a vessel containing a liquid which has an X-ray radiation absorption value approximately equal to living tissue and a plurality of smaller vessels disposed within the vessel and the liquid. A second liquid is disposed within the smaller vessels and has absorption values which are different from the absorption value of the first liquid in the vessel.
U.S. Pat. No. 4,400,827 shows a circular wedge in the form of a ramp or a series of steps which is rotated in synchronism with the frames of film in a photographing means.
A test pattern device for testing scintillation cameras is disclosed in U.S. Pat. No. 4,419,577. The device has a radiation transparent body member with internal mercury-filled communicating passages that define a calibrated radiation opaque test pattern. The body member is formed by securing a plastic cover plate to a plastic base molded with grooves to form the test pattern passages and filling ports, and then sealing the filling ports after mercury has been added to fill the passages.
U.S. Pat. No. 4,460,832 discloses a nuclear radiation attenuator for providing a test image from a source of radiation. The body of the attenuator is formed by a stack of plates aligned in parallel relation to each other and having apertures formed therein. Thus, for example, radiation from a source is attenuated by both plates in a background region without apertures, is attenuated by the first plate in a target region in which only the first plate has an aperture formed, and is attenuated by neither plate in another target region in which both plates have apertures formed.
U.S. Pat. No. 4,472,829 discloses a radiographic phantom for simulating a blood vessel. A base is composed of a non-iodinated material and has a channel formed therein which is filled with a similar material but with minute amounts of iodine suspended uniformly therein to represent a blood vessel.
A radiography calibrating device is disclosed in U.S. Pat. No. 4,497,061 in the form of a sectoral shaped calibration member made up of four layers. In addition to, or instead of being of different thicknesses, the layers may be of different materials. The calibration member is lowered step-wise into the path of a fan-shaped sweep of penetrative radiation so that the amount of radiation that passes through each layer of the calibrating member is monitored by the detecting means.
In order to see what is going on inside the human body, one has either had to perform exploratory surgery or utilize some form of radiography. Now however, more detailed information is being generated by a magnetic resonance imaging scanner. The body is subjected to a powerful magnetic field which aligns the atoms of the body in a north-south orientation. An FM radio signal is transmitted through the body vibrating the molecules until they flip upside down. When the radio signal is terminated, the molecules flip back turning each atom into a tiny FM radio station whose signals are detected by the scanner. In order to calibrate such a machine, a calibration device or phantom must be utilized.